Physics Help Forum Minor head loss
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 Oct 11th 2016, 09:32 PM #1 Junior Member   Join Date: Oct 2016 Posts: 1 Minor head loss Hi, We have done an experiment and measured different pressures in a system, and are required to calculate the minor head loss coefficient K for our working sections. The experiment layout can be seen here: For the gradual working section at the entrance (LHS, where the pipe is beginning to expand), I have ended up with a negative K value. This indicates a head gain, and I am wondering how is this possible? Have I done my calculations incorrectly? Rearranging the energy equation I have the following: K = (P1 - P2)/(500 * V^2) + (V1^2 - V2^2)/V^2, where rho was 1000 and hence divided by 2 to get 500 The values I got were: P1 = 6534.631Pa P2 = 7346.655Pa V = 1.65075m/s (calculated from the pitot tube) V1 = 1.170615m/s (calculated from the flowrate, thus V1 = Q/A1) V2 = 0.169037m/s Using the formula above and these values, you get: K = -0.10359 The diameters are: Pitot: 16mm D1 = 19mm D2 = 50mm I am wondering if I am not understanding something for a practical model? Is the V value I am using correct? I understand there should be some more loss due to major head loss as well as minor loss from the elbow joint, thus lowering this V velocity value, but all that does is decrease my K value further. My calculations for the sudden working section appear to have worked out. tl;dr - Is this negative K simply something I can chalk up to measurement/experimental error, or is there something I'm missing? Thanks in advance!

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